Method of Operating a Washing Machine and Washing Machine

ABSTRACT

A washing machine ( 1 ), is operable in a recirculation washing mode, wherein a filter clogging state of a washing liquid filter ( 13 ) of a recirculation unit is monitored. If a critical filter clogging state is detected, the recirculation washing mode is deactivated and substituted by a non-recirculation washing mode.

The present application is directed to a method of operating a washingmachine and to a washing machine.

In washing machine technology it is well known to recirculate washingliquid in order to reduce consumption of washing liquid, e.g. water.Washing machines operable in such a way are known for example from EP 0240 911 B1, EP 1 204 792 B1 and EP 0 807 707.

Recirculation of washing liquid generally involves a recirculation unitwith a recirculation pump. The recirculation pump extracts washingliquid from a bottom section of the tub of the washing machine and feedsit back into the tub via a spray or jet system arranged above thefilling level of washing liquid.

In order to prevent fluff and other foreign matter from entering andimpairing the function or operation of the pump or jet system, arecirculation filter may be provided upstream the pump.

If such recirculation filters become clogged the washing efficiency ofthe washing machine drastically drops.

By virtue of these facts, it is an object of the invention to provide animproved method of operating a washing machine, in particular avoidingreduced washing efficiency upon recirculation filter clogging. Further,a corresponding washing machine shall be provided.

This object is achieved by independent claims 1 and 8. Embodiments ofthe invention result from dependent claims.

According to independent claim 1, a method of operating a washingmachine which is operable in a recirculation washing mode is provided.The washing machine may be a conventional washing machine, i.e. alaundry washer, or a washer dryer, both of front loading and top loadingtype.

With the method according to the invention, a filter clogging state of awashing liquid filter of a recirculation unit, or of a recirculationcircuit, is monitored or observed, at least from time to time or atcertain time intervals. Advantageously, monitoring of the washing liquidfilter can be carried out continuously during operation of the washingmachine.

If, in the monitoring action, a critical filter clogging state, or theoccurrence of a critical filter clogging state is detected, then therecirculation washing mode is deactivated and substituted by anon-recirculation washing mode.

A critical filter clogging state shall for example pertain to situationsor states in which the washing liquid filter is clogged to such anextent that further operation in recirculation mode would impair washingquality and/or, in particular in the long term, negatively impact thepump of the recirculation unit.

Deactivation and substitution of the recirculation mode shall mean thatexecution of the recirculation mode is blocked, and, even if arecirculation mode has been selected by a user, the recirculation modeis replaced or overruled by a non-recirculation mode. Information aboutblocked recirculation mode may be made available for future operations.For example the information may be stored in a memory, where adeactivation flag may be set. If a critical filter clogging state hasbeen removed and no critical recirculation filter clogging state can bedetermined any more, the recirculation washing mode can be activatedagain, e.g. the deactivation flag may be deleted.

A non-recirculation mode can for example be a conventional washing modein which laundry is tumbled in a washing drum, with the tub being filledwith washing liquid up to a non-recirculation level (e.g. a level higherthan the level in the recirculation mode).

As can be seen, the method can ensure effective washing quality even incases with clogged washing liquid filters in the recirculation circuit.Besides from this, severe damages to the washing machine, in particularthe pump of the recirculation unit, can be greatly prevented. This is ofparticular importance, for example, if the pump acting in therecirculation circuit is also used and adapted for draining washingliquid from the washing machine.

In an embodiment, substitution of the recirculation washing mode by thenon-recirculation mode involves increasing or raising, with respect tothe recirculation mode, a filling level of washing liquid in the tub ofthe washing machine.

Increasing the filling level can involve setting a respective fillinglevel parameter of the washing machine and/or adding additional liquid,for example water, to the tub. Advantageously, the level of the washingliquid being present or to be present in the tub of the washing machineduring operation thereof will be raised.

Setting or providing a respective filling level parameter, for examplein a memory of the washing machine, preferably together withdeactivation information, may be advantageous, as subsequent washingoperations can be based on such information. This means that if acritical recirculation filter clogging state has been detected andrecirculation washing is selected again, the machine automaticallyconducts, preferably after user confirmation, a non-recirculation modeaccording to respective parameters, until critical recirculation filterclogging state is removed.

Further, setting and storing respective parameters and making availablesuch kind of information for subsequent operating phases may beadvantageous if the critical filter clogging state is determined in anidle or non-operating mode or state of the washing machine. This impliesthat the filer clogging state may even be monitored in time intervalswhen the washing machine is carrying out no washing operation or is inan off or standby mode. However, the time window in which a filterclogging state can be determined advantageously depends on therespective method used for detection of filter clogging states.

In general it may be adequate to monitor the filter clogging stateduring recirculation washing phases of the washing machine. However, inan advantageous embodiment in which the filter is used both as arecirculation filter, and as a draining filter for washing liquid,monitoring the filter clogging state in non-recirculation phases may beappropriate.

Increasing the filling level of washing fluid in response to a criticalfilter clogging state safeguards washing quality and efficiency asrecirculation washing modes operate with reduced filling levels ascompared to conventional tumble-only washing modes. With reduced fillinglevels and disabled recirculation, the exposure of laundry to washingliquid is reduced which clearly leads to inferior cleaning efficiencyand may result in excessive wear of laundry or other items tumbling inthe drum of the washing machine. Therefore, if a critical filterclogging state is observed or detected, which leads to deactivation ofthe recirculation unit, additional liquid, such as water, can beautomatically fed to the tub.

The filter clogging state can be monitored by measuring or detecting oneor more representative parameters. For example, the washing liquid flowof washing liquid in the recirculation circuit and/or the washing liquidpressure or pressure change in the tub effected by recirculation washingoperation, in particular a washing liquid pressure drop in an initialphase after activating recirculation washing, and/or at least oneoptically detectable particular feature of the washing liquid filter,can be used as parameters. In using such parameters, the recirculationmode can be deactivated and substituted, if at least one of the measuredwashing liquid flow, measured washing liquid pressure or pressure changeand optically detected particular feature, is indicative of a criticalclogging state.

Advantageously, it is possible that at least one of the measured washingliquid flow, washing liquid pressure or pressure change, in particularpressure drop, is compared to a reference flow value, or referencepressure value or reference pressure change or drop value, respectively.In such cases, a critical clogging state can be determined to exist ifat least one of the following situations occurs: the washing liquid flowis less than or equal the reference flow value, or the washing liquidpressure is higher than or equal the reference pressure value, or thewashing liquid pressure change is less than or equal the referencepressure change value.

In order to improve accuracy, in an advantageous embodiment a criticalfilter clogging state may only be determined to exist if the abovementioned parameters are indicative of a filter clogging state over acertain, in particular extended, period of time or in several successivemeasurements.

In a further embodiment, it is possible, that upon deactivating therecirculation mode during operation of the washing machine, a conduitconnecting a bottom section of the tub of the washing machine to arecirculation unit or recirculation circuit is closed via a valve,preferably a ball valve. In this way, washing liquid can be preventedfrom entering the recirculation circuit. A synergistic effect of usingsuch a valve may be obtained, if a heating element for heating thewashing liquid is arranged upstream the valve. In this case, washingliquid still being present in the deactivated recirculation unit orcircuit downstream the valve will not be heated any more, and henceenergy can be saved.

In an advantageous embodiment, at least one of an event of deactivationof the recirculation mode and occurrence of a critical clogging state ismade available to a user, preferably by at least one of visual andaudible signs. For example, deactivation of the recirculation unit orthe occurrence of a critical filter clogging state may be visuallyindicated on a user interface of the washing machine. Advantageously, awarning or other signals may also be made available to a user if theclogging state of the filter is close to a critical clogging state. Inparticular with such embodiments, it is possible to consider furtherparameters suitable for detecting and/or predicting critical cloggingstates.

As can be seen from the above description, the proposed method providesan improved method for operating a washing machine, and in particular iseffective in avoiding reduced washing efficiency upon recirculationfilter clogging.

According to independent claim 8, a washing machine operable in arecirculation washing mode is provided. The washing machine may forexample be a laundry washer or washer dryer and similar as alreadymentioned beforehand.

The washing machine advantageously comprises a tub, a recirculation unitfor recirculating washing liquid in a recirculation circuit providedwith the tub, and at least one recirculation washing liquid filter. Thewashing machine advantageously further comprises an electronic controlunit adapted to operate the washing machine according to the proposedmethod or any embodiment thereof.

As to advantages and advantageous effects of the washing machine,reference is made to the description above.

In order to implement the proposed method or an embodiment thereof, therecirculation unit may comprise at least one pump for pumping washingliquid in a recirculation circuit. The washing liquid filter canadvantageously be integrated in the recirculation circuit, and arrangedupstream the pump. The washing liquid filter may be adapted to retainlint, loose fibers, dirt particles, impurities and foreign matter fromentering the recirculation pump.

In order to monitor parameters suitable for detecting critical filterclogging states, the washing machine may advantageously comprise atleast one of a flow meter for measuring a washing liquid flow in therecirculation circuit, a pressure sensor, for example a pressure switch,for measuring a washing liquid pressure or pressure change in the tub,and an optical sensor for optically detecting at least one particularfeature of the washing liquid filter. The respective sensors mayadvantageously be connected to the electronic control unit in such a waythat the measured washing liquid flow, measured washing liquid pressureor pressure change or detected particular feature are available foroperating the washing machine accordingly, i.e. for deactivating therecirculation unit if a critical filter clogging state occurs orprevails.

It shall be mentioned, that if it is determined that a critical cloggingstate no longer exists or ceased to exist, advantageously therecirculation washing mode may be activated again.

In an embodiment, in a conduit connecting an opening provided in abottom section of the tub with an input side of the pump, there may beprovided a valve, preferably a ball valve, arranged and adapted to openand close the conduit. Reference is also made to the above discussion.

The washing machine may advantageously comprise a user messaging orinformation unit. This user messaging or information unit may be adaptedto at least one of visually and audibly indicate to a user at least oneof an event of deactivation of the recirculation mode and occurrence ofa critical clogging state. It is of particular interest, to provideaccurate information about filter clogging, preferably announcing filterclogging in advance. Accurate information may advantageously be obtainedby observing one or more parameters and comparing them to at least onerespective reference parameter value or reference parameter.

In a further embodiment, the washing machine may advantageously comprisean integral filter unit having a recirculation filter section anddraining filter section, wherein at least one recirculation washingliquid filter is accommodated in the recirculation filter section. Insuch a configuration, loose fibers or fluff and the like may be rinsedaway from the recirculation washing liquid filter during drainingwashing liquid off the tub of the washing machine. At some instances, itmay well be that an announced or an actually occurred critical filterclogging state can be removed in this way. This enables the washingmachine to be operated in recirculation mode over extended periods oftime.

In a yet further embodiment, the pump may be operable as a recirculationpump and a draining pump, and a valve, preferably a three way valve, maybe provided for connecting the pump either to the recirculation circuitor a draining circuit. In this case, some of the monitored parameters,such as for example a flow of washing liquid through the pump, may beused to identify or forecast also critical draining filter cloggingstates.

The washing machine may comprise a liquid inlet adapted to feedingadditional or fresh liquid to the tub and cooperating with theelectronic control unit such that in the event of deactivation of therecirculation washing mode due to a critical clogging state of therecirculation washing liquid filter, additional or fresh liquid is fedto the tub. In this way, excellent washing results can be achieved evenif the recirculation unit is deactivated.

Exemplary embodiments of the invention will be described in connectionwith the annexed figures, in which

FIG. 1 shows a schematic representation of a washing machine accordingto the invention in a first operational state;

FIG. 2 shows the washing machine of FIG. 1 in a second operationalstate;

FIG. 3 shows a time course of an operational parameter of the washingmachine of FIGS. 1 and 2; and

FIG. 4 shows a filter of the washing machine of FIGS. 1 and 2.

The following description of embodiments shall not be construed aslimiting the scope of the invention. In particular, features jointlyshown in any of the figures can be implemented alone or in any othercombination as discussed further above.

If not otherwise stated like elements are denoted by like referencesigns throughout the figures. The figures may not be true to scale, andscales of different figures may be different.

FIG. 1 shows a schematic representation of a washing machine 1 in afirst operational state.

The washing machine, which in the present case is a laundry washer (butwhich could be as well a washer-drier), advantageously comprises a tub2, in which a drum 3 is rotatably arranged, in order to carry out awashing operation by tumbling items, such as laundry 4, placed in thedrum 3.

The washing machine 1 further comprises an inlet 5 for feeding waterinto the tub 2, preferably via a drawer 6 adapted to accommodate washingagent or washing powder. By feeding water via the drawer 6, the washingagent accommodated therein is flushed into the tub 2. The inlet 5comprises an actuable inlet valve, not illustrated, which, for exampleby virtue of an electronic controller 7 connected thereto, is operableto feed water in accordance with a preset washing liquid level into thetub 2.

The washing machine 1 further comprises a draining unit for drainingwashing liquid from the tub 2. The draining unit comprises a drainingfilter element 8 arranged upstream a draining pump 9. An inlet side ofthe draining pump 9 is connected via the draining filter element 8 to amain conduit 10 in turn connected to a bottom opening 11 of the tub 2.An outlet of the draining pump 9 is connected to a draining conduit 12provided for discharging washing liquid from the tub 2 to an externaldrainage.

The washing machine 1 further comprises a recirculation unit forrecirculating washing liquid. The recirculation unit comprises arecirculation filter element 13 arranged upstream a recirculation pump14. An inlet of the recirculation pump 14 is connected via therecirculation filter element 13 to the main conduit 10. An outlet sideof the recirculation pump 14 is connected to a recirculation conduit 15.A distal end of the recirculation conduit 15 is connected to an opening,in the present case advantageously a top opening, provided in the tub 2in such a way that washing liquid can be sprayed or jetted onto laundrypresent in the tub 2. A jet of recirculated washing liquid isschematically shown in FIG. 1 and depicted by reference sign 16.

The draining filter element 8 and recirculation filter element 13 arepreferably accommodated in a filter unit, in which the draining filterelement 8 is arranged in a draining section, and the recirculationfilter element 13 is arranged in a recirculation section. In a furtherembodiment, not illustrated, the recirculation filter element 13 and thedraining filter element 8 may be two totally independent (i.e. distinct)components and they may be arranged in totally independent (i.e.distinct) filter units or seats.

In between the bottom opening 11 and the filter unit, a ball valve 17may be advantageously provided and adapted to enable and block the mainconduit 10. In a further embodiment, not illustrated, the ball valve 17may be replaced by a different kind of valve, for example a butterflyvalve, a gate valve, an electronic-controlled valve, etc.; more ingeneral any kind of valve adapted to block the main conduit 10 may beused. A branch connecting upstream the ball valve 17 to the main conduit10, preferably comprises a pressostat 18, i.e. a pressure sensor. Thepressostat 18 is adapted and connected to the main conduit 10 such thata washing liquid pressure or pressure change can be determined.

The operation of the washing machine 1 is now described in more detail.FIG. 1 shows the washing machine 1 in a recirculation mode in whichwashing liquid is taken from the bottom section of the tub 2 and sprayedor jetted onto the laundry 4 contained in the drum 3. The flow ofwashing liquid through the recirculation unit is indicated by smallarrows. As can be seen, washing liquid is circulated with the tub 2,preferably, but not necessarily in a continuous way.

Circulation of the washing liquid has the advantage that the amount ofwater needed for conducting a washing programme can be greatly reducedas compared to non-recirculation washing, such as conventional tumblewashing. The recirculation washing liquid level, i.e. the level of thewashing liquid in the tub 2, is indicated in FIG. 1 by reference sign19. As can be seen, due to reduced amounts of washing liquid, thelaundry 4 is not fully immersed in washing liquid. However, sprayingwashing liquid onto the laundry 4 compensates for this. Therefore,excellent washing results can be obtained even with reduced amounts ofwashing liquid.

In particular, as laundry 4 is tumbled by a rotating movement of thedrum 3, fluff, loose fibers, dirt and other foreign particles (typicallycoming from the laundry) will be present in the washing liquid.Obviously, the recirculation filter element 13 intended for protectingthe recirculation pump 14 from fluff, foreign particles and so on isprone to being clogged by respective foreign particles and the like.

Already partial clogging of the recirculation filter element 13 willresult in a reduced recirculation flow impairing washing quality andefficiency. In order to avoid reduced washing efficiency, the washingmachine 1 can monitor the clogging state of the recirculation filterelement 13, and, in particular in the event that a critical cloggingstate occurs, disable or deactivate the recirculation washing unit.

Upon disabling or deactivating the recirculation mode, the washingmachine 1 is set or further operated in a non-recirculation, i.e.tumble-only, mode.

Preferably, along with switching from recirculation to non-recirculationmode, the inlet vale of the inlet 5 is opened and fresh water is fedinto the tub 2 until the predetermined non-recirculation washing liquidlevel 20 (see FIG. 2) is obtained.

The situation after feeding fresh, i.e. additional, water such that thenon-recirculation washing liquid level 20 is obtained, is shown in FIG.2. As can be seen therefrom, and in particular from a comparison of

FIG. 1 and FIG. 2, an enlarged portion of the laundry 4 contained in thedrum 3 is immersed with washing liquid, as is usual fornon-recirculation washing. Thereby washing quality and efficiency isgreatly enhanced as compared to washing results with reducedrecirculating washing liquid levels 19.

Detecting a critical clogging state of the recirculation filter element13 can be implemented, for example, as follows.

The pressure of washing liquid is continuously, or at least at certaintime intervals, measured by the pressostat 18. The pressure can forexample be measured as the height of washing liquid contained in the tub2.

Obviously, if the recirculation pump 14 starts to recirculate washingliquid in the recirculation circuit, the height of washing liquid, andtherefore the pressure measured by the pressostat 18 will decrease. Thepressure decrease or reduction, i.e. the pressure drop, induced byactivation or operation of the recirculation pump 14 is maximal, i.e.the pressure in the tub 2 is minimal, if the recirculation filterelement 13 is not clogged. If the pressure remains above a thresholdvalue, or the pressure drop is smaller than a respective thresholdvalue, a critical clogging state is reached. Thereupon, the electroniccontroller 7, which is advantageously connected to the pressostat 18 andmonitors the pressure or pressure drop, disables the recirculationwashing mode. Then, other operational parameters, such as the washingliquid level, may be advantageously adapted in correspondence withnon-recirculation washing mode requirements. For adapting the washingliquid level, the inlet valve can be activated in order to feedadditional water.

As an example, inter alia depending on the type of washing machine used,a pressure drop of 10-20 mm, corresponding to 10-20 kg/m², may be usedto identify a critical clogging state, if a pressure drop of 25 mm canbe observed in unclogged states of the recirculation filter element 13.In this connection, FIG. 3 shows two diagrams of washing liquid pressureversus time. In an initial time interval, the pressure of the washingliquid has a value of p1 which corresponds to an idle or to anon-recirculation washing mode of the washing machine 1. At a certainpoint of time t_(R) the recirculation unit, and in particular therecirculation pump 14 is activated. Activation of the recirculation pump14 leads to a pressure drop of the washing liquid pressure in the tub 2.In a first pressure drop graph (numbered 24 in FIG. 3), whichcorresponds to a unclogged state of the recirculation filter element 13,the pressure drop Δp′, from p1 to p2, as indicated by a double arrow inFIG. 3, is for example from 70 mm to 45 mm, i.e. 25 mm, corresponding toa non-clogged recirculation filter state.

With increasing clogging of the recirculation filter element 13, theflow of washing liquid in the recirculation circuit is increasinglyblocked, and hence the drop of washing liquid pressure is increasinglydiminished. In FIG. 3, a second, pressure drop graph (numbered 25 inFIG. 3) is shown, which corresponds to a critical clogging state. Due tofilter clogging, a smaller pressure drop Δp″ from p1 to p3 is observed.

In the present case, the washing liquid pressure is observed ormonitored by the electronic controller 7 via pressure values of thepressostat 18. If the pressure drop Δp for example is lower than arespective critical pressure drop value, such as for example lower than10-20 mm, a critical filter clogging state can be assumed. As aconsequence, recirculation operation modes of the washing machine 1 canbe deactivated or substituted as already described further above.

Advantageously, other parameters of the washing machine 1, for exampleof the filter, can be used to identify clogged recirculation filterstates. Such parameters may be for example the flow or flow rate in therecirculation circuit or other recirculation filter parameters, opticalcharacteristics of the recirculation filter element 13 and so on.Preferably respective parameters are selected such that automaticinspection is possible.

In FIG. 4 a filter 21 implementing a recirculation filter element 13 isshown. The recirculation filter element 13 and the draining filterelement 8 preferably are accommodated in a common filter housing 22; inan advantageous embodiment the recirculation filter element 13 and thedraining filter element 8 may be made in a single-piece construction(i.e. they may be obtained as a single component). The respective filterelements are arranged within the housing such that washing liquid passesthe recirculation filter element 13 in recirculation operation mode, andpasses the draining filter element 8 in non-recirculation operationmode.

As is indicated in FIG. 4, the filter meshwork of the recirculationfilter element 13 is preferably somewhat more tight than that thedraining filter element 8. Due to the fact, that both filter elements 8,13 are arranged and adapted in a common housing, washing liquid ofeither recirculation mode or non-recirculation mode may flow through thefilter 21. The washing liquid will be filtered by filter 21 and foreignparticles, dust, fluff or other lint will be retained by either therecirculation filter element 13 in recirculation mode and by thedraining filter element 8 in draining mode. Both filter elements 8, 13shown in FIG. 4 are or can be adapted to efficiently remove foreignparticles from the washing liquid as is required by respective pumps 9,14.

One advantage of the implementation of FIG. 4, i.e. arranging therecirculation 13 and draining filter element 8 in a common housing isthat washing liquid draining via the draining filter element 8 canadvantageously carry away loose fibers, fluff and other foreignsubstances adhering to the recirculation filter element 13. Here, itshall be considered, that the recirculation filter element 13 iscomparatively fine, whereas the draining filter element 8 is comparablecoarse. Hence, fibers, fluff and the like retained by the recirculationfilter element 13 may probably pass through the draining filter element8. Therefore, draining washing liquid from the tub 2 may reducerecirculation filter clogging.

However it is clear that also two completely separated filters andfilter housings may be used.

The filter 21 may advantageously be of exchangeable, preferably ofreusable, type. In case of an exchangeable filter 21, a handle 23 may beprovided at the filter housing 22, for easing replacement of the filter21.

In all, it can be seen, that the proposed method or methods foroperating the washing machine 1 lead to improved operation, inparticular to enhanced and more efficient washing.

1. A method of operating a washing machine operable in a recirculationwashing mode, wherein a filter clogging state of a washing liquid filterof a recirculation unit is monitored, and if a critical filter cloggingstate is detected, the recirculation washing mode is deactivated andsubstituted by a non-recirculation washing mode.
 2. A method accordingto claim 1, wherein the substitution of the recirculation washing modeby the non-recirculation mode involves increasing, with respect to therecirculation mode, a filling level of washing liquid in a tub of thewashing machine.
 3. A method according to claim 2, wherein increasingthe filling level during operation of the washing machine involvesfeeding additional liquid to the tub.
 4. A method according to claim 1,wherein monitoring the filter clogging state involves at least one ofmeasuring a washing liquid flow of washing liquid in a recirculationcircuit, and/or measuring a washing liquid pressure and/or pressurechange in the tub effected by recirculation washing operation and/oroptically detecting at least one particular feature of the washingliquid filter, and wherein the recirculation mode is deactivated andsubstituted if at least one of the measured washing liquid flow, and/ormeasured washing liquid pressure and/or pressure change and/or opticallydetected particular feature is indicative of a critical filter cloggingstate.
 5. A method according to claim 4, wherein at least one of themeasured washing liquid flow, and/or washing liquid pressure and/orpressure change is compared to a reference flow value, and/or referencepressure value and/or reference pressure change value, respectively, anda critical clogging state is determined to exist if at least one of thewashing liquid flow is less than or equal the reference flow value,and/or the washing liquid pressure is higher than or equal the referencepressure value and/or the washing liquid pressure change is less than orequal the reference pressure change value.
 6. A method according toclaim 1, wherein upon deactivating the recirculation mode duringoperation of the washing machine, a conduit connecting a bottom sectionof the tub of the washing machine to a recirculation unit is closed viaa valve.
 7. A method according to claim 1, wherein notification of atleast one of an event of deactivation of the recirculation mode andoccurrence of a critical filter clogging state is made available to auser.
 8. A washing machine operable in a recirculation washing mode,comprising a tub, a recirculation unit for recirculating washing liquidin a recirculation circuit provided with the tub, and at least onerecirculation washing liquid filter, and further comprising anelectronic control unit adapted to operate the washing machine accordingto claim
 1. 9. A washing machine according to claim 8, the recirculationunit comprising a pump for pumping washing liquid in a recirculationcircuit, wherein said at least one recirculation washing liquid filteris provided in the recirculation circuit and arranged upstream of thepump, the recirculation washing liquid filter being adapted to retainlint, loose fibers, dirt particles, impurities and foreign matter fromentering the pump.
 10. A washing machine according to at claim 8,further comprising at least one of a flow meter for measuring a washingliquid flow in the recirculation circuit, and/or a pressure sensor formeasuring a washing liquid pressure or pressure change in the tub and/oran optical sensor for optically detecting at least one particularfeature of the recirculation washing liquid filter, respectivelyconnected to the electronic control unit in such a way that the measuredwashing liquid flow, and/or measured washing liquid pressure and/orpressure change and/or optically detected particular feature areavailable for operating the washing machine accordingly.
 11. A washingmachine according to claim 9, wherein in a conduit connecting an openingprovided in a bottom section of the tub with an input side of the pumpthere is provided a valve arranged and adapted to open and close theconduit.
 12. A washing machine according to claim 8, further comprisinga user messaging or information unit adapted to visually and/or audiblyindicate to a user an event of deactivation of the recirculation modeand/or the occurrence of a critical clogging state.
 13. A washingmachine according to claim 8, comprising an integral filter unit havinga recirculation filter section and draining filter section, wherein atleast said recirculation washing liquid filter is accommodated in therecirculation filter section.
 14. A washing machine according to claim8, wherein the pump is operable as a recirculation pump and as adraining pump, and wherein a valve, preferably a three way valve, isprovided for connecting the pump either to the recirculation circuit ora draining circuit.
 15. A washing machine according to claim 8, furthercomprising a liquid inlet adapted for feeding additional or fresh liquidto the tub and cooperating with the electronic control unit such that inthe event of deactivation of the recirculation washing mode due to acritical clogging state of the recirculation washing liquid filter,additional or fresh liquid is fed to the tub.
 16. A washing machineaccording to claim 9, further comprising at least one of a flow meterfor measuring a washing liquid flow in the recirculation circuit, and/ora pressure sensor for measuring a washing liquid pressure or pressurechange in the tub and/or an optical sensor for optically detecting atleast one particular feature of the recirculation washing liquid filter,respectively connected to the electronic control unit in such a way thatthe measured washing liquid flow, and/or measured washing liquidpressure and/or pressure change and/or optically detected particularfeature are available for operating the washing machine accordingly. 17.A washing machine according to claim 10, further comprising a usermessaging or information unit adapted to visually and/or audiblyindicate to a user an event of deactivation of the recirculation modeand/or the occurrence of a critical clogging state.